Are people who disagree with you inherently evil?

Not really, but it seems that’s what we believe. When others disagree with our opinions we’re likely to attribute negative motives to them:

The research explores the tendency for people to attribute negative motives to others who hold an attitude position that is discrepant from their own. In Studies 1 and 2, American and Canadian respondents indicated their perceptions of U.S. President Bush’s motives for initiating war in Iraq. Consistent with the proposed bias, respondents who disagreed with the war attributed more selfish motivations than did those who supported the war. Study 3 revealed a similar bias when respondents rated the motives of the general citizenry concerning their attitudes about the war, and Study 4 provided evidence of the bias on different attitudinal issues (e.g., abortion and gay marriage). Study 4 also indicated that biased attributions of motive were primarily confined to respondents who were highly involved in the attitude issue. Discussion centers on naïve realism, social identity concerns, and attitude justification as relevant underlying theoretical factors.